Was it just me that thought Michael's reaction to his young brothers death was a bit extreme, to want to blow his own brains out within seconds of him dying?

Not really. The world is dead, it's gone, there's nothing left. All he has is his brother, the two of them surviving and making their way through this world, it's all that ties him to it. With him gone, what is left...? What is the point?

Regarding Ellie's OK, she knows, but how the end made me feel was that by lying, and making this massive sacrifice, Ellie knows Joel cares about her deeply. Everyone she's ever cared about has died, or, as she put it, "left her". Joel made a very extreme decision to save her, and stays with her, and while I think she doesn't approve of the decision, it has made her feel cared for and loved.

I guess the ending and run up to it are defined by how much of a connection you made to the characters. If you look at it from a pragmatic POV, Joel is a dick, he has doomed mankind, etc. I feel really immersed, I think they did such a wonderful job of telling this story and fleshing out these characters, even in little ways. I wanted nothing more than to save Ellie and just run the hell out of that place (and yes, I killed the doctors too). Game made me a little teary a few times, maybe I'm a softie.

The giraffe section was extremely well done, but more so it highlighted how well the rest had been put together until that point. If you hadn't felt the despair and the connection to this world, seeing this uninfected ray of hope out of nowhere wouldn't have had the same impact.

Just flat out loved it. I want to NG+ it, but part of me just wants to leave it at that, their story was told.